The present invention relates to an optical recording medium including recording tracks for recording a signal, which are made up of at least either one of grooves and lands, and an optical recording and reproducing device using this optical recording medium as well as a recording and reproducing method for the optical recording medium.
In recent years, for rewritable high-density optical recording media, and in particular magneto-optical recording media, there has been propose d and widely adopted such a format as to realize a large storage capacity ranging between 5 GB and 7 GB on one side of a disk having a diameter of 12 cm which is a common size of a CD. In that case, the thickness of a disk plate is reduced to 0.6 mm so as to allow an optical pickup to have a numerical aperture NA=0.6. Moreover, a single plate structure is adopted to attain magnetic field modulation, where a recording/reproducing laser wavelength xcex=630 nm to 650 nm, a track pitchxe2x88x920.6 xcexcm, and recording line density=0.20 xcexcm/bit.
As a recording format to realize the above large-capacity recording is adopted a land/groove recording system which is capable of recording and reproducing a signal in both lands and grooves, and is effective in attaining high density.
As an example of techniques to attain the high-density optical recording medium using this recording format, a technique disclosed in Japanese Unexamined Patent Publication No. 73685/1999 (Tokukaihei 11-73685 published on Mar. 16, 1999) is known. An optical recording medium according to the publication 11-73685 has an arrangement in which: at least either one of a groove and a land has interrupted portions, or xe2x80x9cclock marksxe2x80x9d, where the groove or land is interrupted at predetermined intervals (the interrupted portions of a predetermined length); a beam spot is set to scan in a peripheral direction of a track so as to generate a tangential push pull signal (hereinafter referred to as xe2x80x9cITPP signalxe2x80x9d) from the clock mark; and the TPP signal thus generated enables a clock signal to be discharged. Particularly, in this optical recording medium, it is proposed that an effective control signal which causes little jitter when the length of the interrupted portion is larger than 0.8 xcexcm which is a recording/reproducing laser spot size.
However, in order to perform recording and reproducing of an optical recording medium, it is necessary to record such control signals as a clock signal and the like for synchronization of an information signal, and to downsize a recording region for the control signal so as to attain high density.
Further, the above publication only discloses a relationship between a gap length and a sum signal in an optical recording medium having the interrupted portions at predetermined intervals (interrupted portions of the predetermined length), i.e., xe2x80x9cgapsxe2x80x9d, in either one of a land and a groove, and a relationship between the gap length and a TPP signal is not discussed. Furthermore, the above publication discloses neither a relationship between a clock mark length and a TPP signal nor a relationship between the clock mark length and a sum signal in connection with the optical recording medium having the interrupted portions (clock marks) of the predetermined length in the land and groove, respectively.
As a result of researches, the inventors of the present application have discovered that the waveform of a TPP signal is distorted when, for example, a clock mark length exceeds a beam spot size. Specifically, when the clock mark length exceeds the beam spot size, the distortion of the waveform of the TPP signal becomes large at a zero cross point in particular, that causes a problem of increasing a detection error in the clock signal.
Further, in a method of detecting an address signal by one-side wobble, the address signal is detected by a push pull (PP) signal. However, the one-side wobble outputs not only the PP signal but also a TPP signal. The TPP signal here is an address leakage signal. When the address leakage signal has an amplitude which is not smaller than an amplitude of the TPP signal for detecting a clock signal, there arises a problem that such an address leakage signal is erroneously detected as a clock signal.
The present invention has been attained so as to solve the foregoing problems, and an object of which is to provide an optical recording medium, an optical recording and reproducing device and a recording and reproducing method for the optical recording medium, that are capable of (i) high-density recording and reproduction by reducing a region to record a control signal, (ii) reproduction of the control signal having a waveform free from distortion by appropriately setting a relationship between the length of a clock mark to obtain the control signal and the size of a beam spot to be emitted to the clock mark, and thereby (iii) generating a clock signal in a state of little jitter.
In order to attain the foregoing object, an optical recording medium according to the present invention has an arrangement in which a groove and/or a land composing a recording track includes an interrupted portion of a predetermined length in a direction of the recording track, and the interrupted portion is a control signal mark, such as a clock mark, to obtain such a control signal as a clock signal, wherein: when, by the length of the control signal mark and a spot size of a laser to be emitted to the recording track, (the length of the control signal mark)/(the spot size of the laser)=CM, CMxe2x89xa61.0.
The control signal mark is reproduced by an optical pickup, thereby obtaining, for example, a tangential push pull (TPP) signal. From the TPP signal is generated a control signal, such as a clock signal.
The inventors of the present application studied a relationship between the control signal mark length and the laser spot size that enables a control signal generating TPP signal free from distortion to be obtained, and discovered the foregoing relationship. More specifically, by setting so that CMxe2x89xa61.0 when (the control signal mark length)/(the laser spot size)=CM, it was possible to obtain a control signal generating TPP signal free from distortion. This enables generation of a control signal in a state of little jitter.
Further, by setting the control signal mark length and the laser spot size to establish the foregoing relationship, a necessary control signal mark length can be shortened. Consequently, in the optical recording medium, a region to record a control signal is reduced, thereby enabling high-density recording and reproduction.
Further, an optical recording and reproducing device according to the present invention uses an optical recording medium in which a groove and/or a land composing a recording track includes an interrupted portion of a predetermined length in a direction of the recording track, and the interrupted portion is a control signal mark, such as a clock mark, to obtain such a control signal as a clock signal, wherein: when, by the length of the control signal mark and a spot size of a laser to be emitted to the recording track, (the length of the control signal mark)/(the spot size of the laser)=CM, CMxe2x89xa61.0, the optical recording and reproducing device including: a threshold value setting section for setting such a threshold value as to detect a control signal which was obtained from the optical recording medium at least based on an amplitude of the control signal; a control signal detecting section for making a comparison between the control signal and the threshold value so as to detect a control signal; and a control signal generating section for generating a new control signal based on the control signal detected by the control signal detecting section.
With this arrangement, since CM is set so that CMxe2x89xa61.0, it is possible to obtain a control signal free from distortion from the control signal detecting section, thereby enabling the control signal generating section to generate a new control signal in a state of little jitter.
Further, a recording and reproducing method for an optical recording medium according to the present invention is capable of performing recording and/or reproduction of information with respect to an optical recording medium in which a groove and/or a land composing a recording track includes an interrupted portion of a predetermined length in a direction of the recording track, and the interrupted portion is a control signal mark to obtain a control signal, wherein: when D is a laser spot size of laser light to be emitted to the optical recording medium, and C1 is the length of the control signal mark, it is set to satisfy 0.66xc3x97Dxe2x89xa6C1 xe2x89xa60.72xc3x97D.
The control signal mark is reproduced by an optical pickup, thereby obtaining, for example, a tangential push pull (TPP) signal. From the TPP signal is generated a control signal, such as a clock signal.
In the case where a reproducing signal from the optical pickup is used to detect the control signal generating TPP signal, the amplitude of the reproducing signal from the optical pickup is compared with a predetermined threshold value, thereby discriminating the control signal generating TPP signal. In that case, in order to accurately perform the discrimination, it is preferable to increase the amplitude of the control signal generating TPP signal.
Accordingly, the inventors of the present application studied a relationship between the control signal mark length and the laser spot size that can increase the amplitude of the control signal generating TPP signal, and discovered the foregoing relationship.
More specifically, by setting to satisfy 0.66xc3x97Dxe2x89xa6C1xe2x89xa60.72xc3x97D when D is a laser spot size of laser light to be emitted to the optical recording medium, and C1 is the length of the control signal mark, it was possible to obtain a control signal generating TPP signal having a large amplitude. This makes it possible to obtain a desirable control signal surely and in a state free from distortion.
Further, by setting the control signal mark length and the laser spot size to establish the foregoing relationship, a necessary control signal mark length can be shortened. Consequently, in the optical recording medium, a region to record a control signal is reduced, thereby enabling high-density recording and reproduction.